WEIR, or WEAR, is a dam erected across a river, either for the purpose of taking fish, of conveying a stream to a mill, or of maintaining the water at the level required for the navigation of it.
The erection of weirs across public rivers has always been considered a public nuisance. Magna Charts (c. 23) directs that all weirs for the taking of fish should be put down except on the sea-coast. By the 12 Edw. IV. c. 7, and other subsequent acts, weirs were treated as public nuisances, and it was forbidden to erect new weirs, or to enhance, straighten, or enlarge those which had aforetime existed. Hence in a case where a brushwood weir across a river had been converted into a stone one, whereby the fish were prevented from passing except in flood-time, and the plaintiff's fishery was injured, this was considered to be a public nuisance, although two-thirds of the weir had been so converted without interruption for upwards of forty years.
And it was laid down in that and other cases, that though a twenty years' acqui escence might bind parties whose private rights only were affected, yet that no length of time can legitimate a public nuisance. (7 East, 198; 2 B. & Ald. 662.) On the same grounds it will probably be held that the Prescription Act (2 and 3 Wm. IV. c. 71) does not apply to weirs. It appears therefore that no weirs can be maintained on any rivers to the prejudice of the public, or even, as it seems, of in dividuals, except such as have existed time out of mind, or such as have been erected under local acts of parliament for the navigation of particular rivers.
The provision of the Roman law as to the maintenance of public rivers (flumina publica) against any impediment to navi gation, or against any act by which the course of the water is changed, are con tained in the Digest (43, tit. 12, 13).